This invention relates to an arrangement for supplying those input data signals to a plurality of central processing units which may be first or original data signals supplied from signal sources and second data signals resulting from data processing carried out by the central processing units or even third data signals derived from signal sources and central processing units placed at a remote location. The arrangement according to this invention is particularly suited for use in putting a plurality of central processing units into cooperation to carry out supervision and control over an electric power system as described in U.S. patent application Ser. No. 386,382 filed by Toshio Takagi, one of the present joint inventors, on Aug. 7, 1973, assigor to Tokyo Denryoku Kabushiki Kaisha, one of present assignees. U.S. application Ser. No. 386,382 was abandoned in favor of continuation application Ser. No. 562,452 filed Mar. 27, 1975. This invention will therefore be described in the following in specific conjunction with an electronic data processing system for protecting an electric power transmission system.
As the power dealt with by electric power transmission systems has grown and is still growing larger, it is the general tendency that high speed and high reliability are progressively required to protect the systems and to detect and dispose of a trouble that has happened to occur in the systems. In extra-high tension transmission systems, the protection must more fully be insured. In order to cope with these requirements for high speed and reliability, electronic data processing has been introduced in supervision and control of large-power or extra-high tension electric power systems. It is, however, to be pointed out that the data to be dealt with by the electronic data processing system are continuous and that a large number of data must be dealt with per unit time. By way of example, the data to be dealt with for a substation in an electric power system are instantaneous values of voltages and currents of the power line, bus bar, transformer, and the like to be protected and the states of on-off of the circuit breakers and line switches and tap points of the voltage regulators. It is desired at present to resort to a plurality of central processing units for respective manners of data processing because the data processing must be carried out on these data signals at a high speed. For instance, the central processing units are preassigned to main protection of the transmission line, backup protection thereof, protection of the bus bar, protection of the voltage regulators, and so forth. It becomes now necessary that the central processing units share the first data signals mentioned above and those second data signals that result from data processing carried out by the same and/or other central processing units, so as to produce desired output signals for enabling the transmission line, bus bar, or voltage regulator protection devices to operate.
On coupling two central processing units for cooperation, it has been the practice to select one thereof as the master processor for producing write-in commands and the other as a slave processor for carrying out the write-in operation in compliance with the write-in commands. More particularly, first data signals representative of the instantaneous value of voltages and currents and the states of on-off and tap points may be supplied to both processors. On supplying the second data signals representative of, for example, the effective values of the voltages and currents produced by the master processor to the slave processor, the master processor delivers a write-in command to the slave processor. The slave processor thereupon goes to trap or carries out interruption of the program, namely, suspension of the program being executed. After the interruption is carried out, the slave processor notifies the master processor of the fact that the slave processor is ready for write-in of the second data signals which the master processor will supply. The master processor now delivers the data signals to the slave processor to make the latter write-in the data signals. When the number of the central processing units is two, it is relatively easy thus to supply the first and second data signals to the central processing units to make them carry out the desired data processing. It turns, however, difficult to make three or more central processing units carry out the desired data processing because not only an increasing number of connections become necessary but also the software for interruption of programs becomes complicated. This results in additional disadvantages of reduced speed and reliability. In some cases, local electronic data processing systems are installed at various points of a large-scale electric power system and a central station carries out supervisory control of the power system through the local data processing systems. In such a supervisory control system, it becomes additionally necessary to supply the third data signals mentioned at the outset of the instant specification to the central processing units of each data processing system. This renders the problems of coupling the central processing units more serious.